A number of diverse types of video display systems have been developed for use with, for example, television receivers, and as video output devices for computer systems and in systems for monitoring and controlling processes in factories. Many video display systems make use of cathode ray tubes, in which a beam of electrons is directed to a display screen to energize phosphors deposited thereon. The phosphors, when energized, emit light of predetermined colors. The electron beam is scanned line-by-line in a raster format across the screen, selectively energizing the phosphors in a pattern defining the image. The intensity of the electron beam is varied, which, in turn, varies the intensity with which the scanned phosphors are energized, to thereby create an image on the screen.
Cathode ray tube video display systems require a significant amount of power to generate and control the electron beam, and they generate quite a bit of heat. In addition, the geometry of the arrangements in the cathode ray tubes that generates the beam normally places a limit on the height and width of the screen that can be accommodated, in relation to the depth of the video display system. More recently, liquid crystal displays have been developed which require substantially less power, and so are often used in, for example, portable battery-operated computers, where power conservation is important. In a liquid crystal display, the image is developed, not directly by generating light having a particular pattern, but instead by creating shadows across a uniform light source, with the shadows defining the pattern required for the image. The shadows are created by devices known as "liquid crystals", whose capability of transmitting light varies with an applied electrical charge. A liquid crystal display system includes a large number of such liquid crystals in a rectangular array, with one liquid crystal being present for each picture element, or "pixel", on the screen. Each liquid crystal is controlled individually, which often results in a complex control circuitry. In addition, the liquid crystal display does not require any arrangement such as is required to generate the beam in a cathode ray tube, and so they can be much thinner, and be able to use less power. As a result, liquid crystal display systems are limited to very small screens.